Because the little ones need more food to grow, just like teenagers- they are always hungry. The big ones are holding eggs/milt and are just worried about breeding. Seems after spawning time and the post spawn blues, the big ones are less effected by cold fronts.
Maybe it’s some phenomenon only I’m seeing or I’m just crazy and seeing things, but I’ve observed keeper sized and bigger fish following or just gently nipping the tails of baits, spring and summer, after a cold front. I’m also seeing the smaller fish becoming more active, even hitting on top waters during this time. The odd thing is that a lot of these more active small fish are often dinks and prior to the post frontal conditions, I wasn’t catching these dinks. It’s seems as if small fish are becoming more active with a larger strike window while the larger fish are becoming far less active an in a negative feeding mood right after a cold front. Sorry for the hijack.